An electronic device needs some form of electric power supply to work. For many electronic devices, particularly portable devices, batteries are preferred over a cord-connection to a mains outlet. While it is possible to change batteries to a fresh set when the charge has drained, it is common practice in many cases to instead make use of re-chargeable batteries. Such batteries may be re-charged using a battery charger connected to a mains outlet.
A battery charger therefore typically includes an interface including a plug connectable to a mains outlet, AC/DC converter electronics arranged in a protective housing, from which housing the plug projects, and a battery interface comprising a connector exterior of the housing. The plug is connected to the AC/DC converter means in the housing for supplying an AC current thereto, and the AC/DC converter means are in turn connected to the battery connector for supplying a DC charging current to a connected battery. The AC/DC converter electronics may be more or less advanced, and may e.g. include a control unit for implementing a predetermined charging scheme adapted to a certain type of battery. In many cases, though, the actual charging control circuitry is instead included in a device carrying the battery, such as a mobile phone, to which device the battery connector is connected. In such solutions, the battery charger is a fairly simple device. The battery interface can include a battery connector comprising a plug or socket for direct attachment of the battery or battery-carrying device, or include a cord having such a plug or socket at its remote free end.
For many electronic devices, a battery charger is supplied when the device is purchased, or may be provided separately. Furthermore, many types of electronic devices and chargers are produced for a global market with little or no difference between different regions or countries. The battery charger is therefore generally a low cost product produced in millions of units, and often supplied all over the world for use in places with varying mains voltage. Battery chargers are also often totally insulated products, for the purpose of avoiding humidity on the converter electronics.
However, in some parts of the world it is more or less common with an irregular, uneven mains voltage, which in extreme conditions may cause a rapid development of heat and gas production inside the charger. This process may be almost instantaneous and the developed gases may not escape out quickly enough from the housing of the charger. Since chargers are often provided for use with portable devices, such as mobile phones, laptop computers, pocket computers and so on, also the chargers are preferably very small for good portability. Furthermore, the smaller the charger, the smaller the space defined within its housing, which tends to result in an even more rapid increase in pressure due to the small enclosed volume. In serious cases, this may lead to a risk of explosion in the charger with subsequent damage to the charger equipment.